A thick layer of haze has settled over Denver as a result of the massive wildfires in southern California. This view of downtown Denver was photographed from 84th Avenue at Clay Street in Westminster. A plane towing a banner is seen above the city skyline.

Heavy smoke flowing into Colorado from fires in California and Utah has created unhealthy breathing conditions for some people, the state health department said today.

A smoke health advisory was issued this afternoon for Garfield County and parts of northwest and north-central Colorado. The air is filled with so many fine particulates that state health officials said the air quality is in the “unhealthy for sensitive group” category, which includes individuals with heart disease, respiratory illness, the very young and very old.

The highest concentrations of smoke are likely occur north of Interstate 70 and as far east as the Front Range.

Although the air in the metro region is hazy, officials at the Colorado Department of Public Health and Environment said particulate levels outside the warning areas are only moderate.

Pat Reddy, a meteorologist with the department’s Air Pollution Control Division, said that if visibility is less than 5 miles in a neighborhood, smoke has reached an unhealthy level.

“When smoke is thick or becomes thick in your neighborhood, remain indoors,” said Reddy. “This is especially true for those with heart disease, respiratory illnesses, the very young and the elderly.”

Reddy said people should consider limiting their outdoor activity.

He said he expects the smoke to begin to diminish in many areas this evening, although the situation will have to be evaluated tomorrow.

Forecasters at the National Weather Service, however, said that smoke from fires in California and Utah, as well as smaller fires in Colorado, will cloud the skies with haze possibly into Sunday.

As of 2:45 p.m., the foothills and mountains to the west of Denver could not be seen from downtown because of smoke.

The air is so hazy in parts of Boulder County that the Boulder County Sheriff’s Department has been receiving 911 reports of smoke, according to Commander Rick Brough.

Joe Ramey, a meteorologist with the National Weather Service in Grand Junction, said that a high-pressure system is continuing to pump smoke from several California fires and 17 fires currently burning in Utah into the state. He said a fire near Nucla in south-central Colorado also may be contributing to the haze.

Most of the smoke, however, is being generated by the 190-square-mile fire burning near Los Angeles, he said.

He said smoke relief may come for portions of the state sometime Saturday as a chance of rain is expected. But it will linger into Sunday in eastern Colorado, he predicted.

“As far as clearing out, we are going to see a slow erosion of the smoke,” said Ramey.

Bob Koopmeiners, a meteorologist with the National Weather Service in Boulder, said the smoke from California is coming into Colorado “in a direct line” from the California fires.

He said the smoke could begin to clear as early as Thursday.

On Monday, Norv Larson, another meteorologist with the National Weather Service, said the smoke is rising about 12,000 feet above Denver and Grand Junction, or 17,000 feet above sea level. He said it has yet to reach the jet stream, which flows at an altitude of about 20,000 feet.

Forecasters said the smoke may cause surface temperatures to drop about one to three degrees in the affected areas.

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